We were on Oahu last year at the Marriott resort in Ko'Olina and rented a car. The problem (maybe not a problem) with Ko'Olina is that it is pretty isolated. If you want groceries or other eating options apart from the resorts you really need a car. Driving around Oahu is pretty easy even into Waikiki.
We did the Pearl Harbor thing last year. It takes all day, if you want to see everything, and even then we couldn't finish everything. The best bet is to get there early. They tours to the Arizona are on a first come first serve basis. We arrived about 1 hour after they started handing out the tickets and our "time" was 2.5 hours later. It ended up working out as we toured the museum and the WWII submarine that is also there. After we got back from the Arizona we went and toured the other battleship (Mighty Mo, I think) that is there. However, we missed the aviation musuem as we were just too tired from standing/walking all day.
It is a wonderful experience but does take a long time. I would have hated to be hemmed in by a tour bus time or a tour group. It was easy and great to be able to explore on our own. I could actually go back again as there is just so much to see.
Getting there was pretty easy but ask for directions. We followed a guide book and initially went towards the base entrance and not the Pearl Harbor visitor area. Once we figured it out all was well.
I wouldn't worry about driving around Oahu, after all it is an island you can't get lost for long!!!